1. Field of the Invention
The present invention relates generally to inductive amplifiers used to identify and trace a particular wire within a group of wires, and more particularly, to an inductive amplifier having an automatic gain control for reducing the gain of the inductive amplifier whenever an external butt set is coupled to the inductive amplifier.
2. Description of the Relevant Art
Inductive amplifiers, or tone detectors, are high impedance amplifiers used by telecommunications service personnel to identify and trace a particular pair of wires within a group or bundle of wires, without damaging the insulation surrounding each of such wires. Such inductive amplifiers are commonly used in conjunction with tone generators for tracing wires. The tone generator is coupled with a particular pair of wires of interest to inject a distinctive audio frequency tone within such wires. Typical audio tone generators are capable of providing two different tones within two different frequency ranges. A first, or lower, tone is provided within the frequency range of 500 Hz. to 1100 Hz. A second, or higher, tone is provided within the frequency range of 800 Hz. to 1600 Hz. The output of the tone generator can provide one of such tones continuously, or can be caused to rapidly switch between the lower and higher tones to produce a warbled output tone. Accordingly, most inductive amplifiers are designed to be responsive to frequencies within the range of approximately 300 Hz. to 3,000 Hz.
During use, the probe tip of the inductive amplifier is placed adjacent one of several wires to identify the particular pair of wires conducting the injected audio tone. The inductive amplifier typically includes a built-in loudspeaker which can be used to produce an audible signal derived from the injected audio tone. In addition, terminals may be provided for allowing a rugged service telephone handset, or buttset, to be attached to the inductive amplifier to reproduce the detected audible tone in the earphone of the buttset.
When a user of an inductive amplifier is not using a butt set therewith, the internal speaker of the inductive amplifier must be driven with a relatively high volume output signal so that the tone emitted by the internal speaker can be heard over background sounds when the inductive amplifier is held at arm's length. However, when using a butt set, a service technician usually holds the earpiece of the butt set adjacent the user's ear. Unless the volume knob of the inductive amplifier is adjusted, the volume of the sounds produced in the earpiece of the butt set is likely to be too high and irritating.
In addition, the connection leads of a typical butt set are approximately six feet long and are unshielded. Accordingly, the attachment of butt set leads can serve to introduce noise, feedback, or other stray signals into the inductive amplifier circuitry, particularly when the gain of the inductive amplifier is set to a high level; these signals can cause instability and oscillations within the inductive amplifier, making it more difficult or impossible for the user to discern the desired signal tone output by the tone generator.
Accordingly, it is an object of the present invention to provide an inductive amplifier which includes both a built in speaker and butt set terminals to facilitate the connection of the leads of a butt set, and which automatically reduces the gain of the output signal when a butt set is connected to the inductive amplifier.
It is another object of the present invention to provide such an inductive amplifier which lessens the likelihood of instability and/or oscillations within the inductive amplifier when a butt set is connected thereto.
It is still another object of the present invention to provide such an inductive amplifier which can be manufactured easily and inexpensively.
These and other objects of the present invention will become more apparent to those skilled in the art as the description of the present invention proceeds.